I can't figure it out what is wrong here. I am getting the error "Can't get the length of the 'Hand' ". Any suggestions?

import random


class Die:
    def __init__(self, sides=2, value = 0):
        if sides < 2:
            raise ValueError("Can't have fewer than two sides")
        self.sides = sides
        self.value = value or random.randint(1, sides)

    def __int__(self):
        return self.value

    def __add__(self, other):
        return int(self) + other

    def __radd__(self, other):
        return self + other

    def __repr__(self):
        return str(self.value)

    def __len__(self):
        return len(self)

class D20(Die):
    def __init__(self, sides = 2):
        super().__init__(sides = 20)

from dice import D20

class Hand(list):
    def __init__(self, size = 2, die_class = D20, *args, **kwargs):
        self.die_class = die_class
        self.size = size
        super().__init__()

    @property
    def total(self):
        return sum(self)    

    def roll(self, input):
        if not isinstance(input, int):
            raise ValueError("Input must be a whole number")
        for _ in range(input):
            self.append(self.die_class())
        return self